1) Field of the Invention
The present invention relates to a thermal transfer dye image-receiving sheet. More particularly, the present invention relates to a thermal transfer dye image-receiving sheet capable of recording clear dye images thermally transferred from a dye sheet in a high color depth at a high sensitivity.
2) Description of the Related Arts
Currently there is an enormous interest in the rapid development of new types of thermal transfer color image printer, for example, a color and copier, capable of recording high quality color images by a dye thermal transfer system.
In the dye thermal transfer printer, colored images are formed by superimposing a dye ink sheet composed of a substrate sheet and a yellow, cyan or magenta dye ink layer formed on the substrate sheet, and comprising a mixture of a sublimating dye with a binder on a dye image-receiving sheet composed of a dye image-receiving resinous layer formed on a substrate sheet in such a manner that the dye ink layer surface of the dye ink sheet is brought into direct contact with the dye image-receiving resinous layer of the dye image-receiving sheet, and the dye ink layer is locally heated by a thermal head of a printer, to thermally transfer the yellow, cyan or magenta dye images to the dye image-receiving resinous layer. In this thermal transfer of the colored images, the heating of the thermal head is continuously controlled in accordance with electrical signals corresponding to the pattern of images to be recorded, and the amount of dye transferred from the dye ink layer to the image-receiving resinous layer is continuously controlled in accordance with the amount of heat, and heating time, applied by the thermal head, to thereby print out continuous tone full color images having a desired color depth (darkness) on the image-receiving resinous layer.
To record high quality colored images having an excellent clarity on the image-receiving sheet, it is necessary to provide a dye image-receiving resinous layer which will not be melt-adhered to the dye ink sheet, is capable of receiving dye images having a high resistance to light and heat, at a high transferring speed, and exhibits a high affinity to and capacity for receiving the thermally transferred dye.
In particular, the thermal transfer dye image-receiving sheet usable for the dye thermal transfer recording system must be provided with an image receiving layer comprising, as an active principle, a thermoplastic resin capable of being dyed with a sublimating dye supplied from a dye ink sheet.
For example, Japanese Unexamined Patent Publication No. 60-24,996 discloses an image-receiving sheet having an image-receiving resinous layer comprising a polyvinyl chloride resin which contains a plasticizer, and thus is capable of receiving dye images with a high color depth and a high color fastness to light.
Nevertheless, it should be noted that the dye images recorded on an image-receiving sheet must have not only a high color depth and light fastness but also a high resistance to heat and to diffusion, and an excellent storage durability.
Generally, in the production of the image-receiving sheet, a coating liquid is prepared by dissolving or dispersing a dye-receiving resin in an organic solvent and then applying the resultant solution to a surface of a substrate sheet by a customary coating device, for example, a mayer bar, to thus form an image-receiving resinous layer. In view of the above-mentioned process, the dye-receiving resin must have a high solubility or dispersibility in the organic solvent, but the polyvinyl chloride resin has an unsatisfactory solubility in the organic solvent and is disadvantageous in that the plasticizer easily oozes out to the outer surface of the dye-receiving resinous layer. Accordingly, an improvement of the properties of the polyvinyl chloride resin for the image-receiving resinous layer is needed.
In another example, Japanese Unexamined Patent Publication No. 63-51,181 discloses an image-receiving resinous layer comprising, as an active principle, a vinyl chloride and vinyl acetate-based copolymer. This image-receiving resinous layer effectively enhances the light fastness of the dye images received thereon, but has an unsatisfactory dye-receiving sensitivity.
In still another example, Japanese Unexamined Patent Publication discloses an image-receiving resinous layer comprising a cross-linked thermoplastic polyester resin having an enhanced resistance to melt adhesion, but this melt adhesion resistance has proved unsatisfactory when the thermal head used has a special form and a temperature imparted to the image-receiving resinous layer by the thermal heat or the ambient temperature is relatively high.